A background art is explained with reference to a shovel as an example.
A hybrid shovel includes an engine, and a generator motor and a hydraulic pump that are connected to the engine. The hydraulic pump drives a hydraulic actuator by discharged oil of the hydraulic pump. On the other hand, the generator motor operates as a generator by the power of the engine to thereby charge an electric storage device and timely operates as a motor by the electric power of the electric storage device to thereby assist the engine.
In the hybrid shovel, a connection (power transmission) structure of the engine, the generator motor, and the hydraulic pump that configure a power unit is disclosed in, for example, Patent Document 1.
The structure described in Patent Document 1 includes a flywheel attached to a crankshaft of the engine. The flywheel is directly coupled to a rotor shaft of the generator motor by bolts. The rotor shaft is supported by a bearing provided in a motor housing of the generator motor. Consequently, the flywheel and the rotor shaft are supported in two places, i.e., a supporting portion by the bearing of the crankshaft and a supporting portion by the bearing of the rotor shaft. In this state, the rotor shaft and a pump shaft are spline-coupled.
However, when the rotor shaft is independently supported by the bearing as described in Patent Document 1, the rotor shaft needs to be increased in length by the length of the supporting portion by the bearing. Therefore, the lengths of coupling portions of the flywheel, the rotor shaft (a rotor), and the pump shaft increase, and therefore the axial length of the entire power unit increases.
Therefore, the configuration described in Patent Document 1 is disadvantageous, in particular, in a shovel in which a space (an engine room) for disposing a power unit is limited.
Note that, in the structure described in Patent Document 1, in order to reduce the axial length, it is conceivable to omit the bearing that independently supports the rotor shaft. That is, it is conceivable to change the structure into a structure in which the flywheel and the rotor shaft are supported in a cantilevered manner only in the supporting portion by the bearing of the crankshaft.
However, the axial length is reduced only a little by simply omitting the bearing, which supports the rotor shaft, without changing the structure described in Patent Document 1. Therefore, when the structure described in Patent Document 1 is changed to a structure in which the flywheel and the crankshaft are supported in a cantilevered manner, a bending moment applied to the crankshaft becomes excessive. Consequently, insufficiency of strength of the crankshaft and the like is caused or an adverse effect that the strength of the crankshaft and the like has to be substantially increased occurs.    Patent Document 1: Japanese Unexamined Patent Publication No. 2008-7023